Proteomic markers of colorectal cancer risk: results from the European Prospective Investigation into Cancer and Nutrition

The human body is a complex machine that constantly signals its state through the chemicals flowing in the blood. Among these chemicals are proteins, the tiny workhorses that build tissues, fight infections, and keep cells functioning. When something goes wrong, such as a cancer beginning to grow, the body often changes the amount of these proteins long before a tumor becomes large enough to be seen on a scan or felt by a doctor. Scientists have long hoped to find specific proteins that act as early warning signs for colorectal cancer, a disease that affects the large intestine. However, for a long time, researchers treated the entire large intestine as a single unit, grouping together cancers that start in the colon and those that start in the rectum. This approach ignored a crucial fact: these two areas, while neighbors, are biologically distinct. They develop differently, respond to treatments in different ways, and likely have different warning signals. Understanding whether the body sends the same distress call from the colon as it does from the rectum is essential if we hope to create better tests for early detection.

A team of researchers set out to solve this puzzle by looking at the blood of thousands of people over many years. They focused on the European Prospective Investigation into Cancer and Nutrition, a massive study that has followed more than half a million people across ten European countries since the 1990s. From this group, they selected a specific subset of individuals who had donated blood samples before they were diagnosed with cancer. The researchers used a high-tech method to measure nearly 6,400 different proteins in these blood samples. They then tracked who developed cancer over the next decade, comparing the protein levels of those who got sick with those who remained healthy. The goal was to see if certain proteins were consistently higher or lower in people who would eventually develop cancer, and to see if these signals differed depending on where the cancer started.

The results revealed a clear and surprising distinction. When the researchers looked at colorectal cancer as a single group, they found 36 proteins that seemed to be linked to the disease. However, when they separated the data to look at colon cancer and rectal cancer individually, the picture changed dramatically. The signals for colon cancer were strong and numerous, with 50 different proteins showing a clear connection to the risk of developing the disease. In stark contrast, the signals for rectal cancer were almost non-existent; only two proteins showed a link, and none of the proteins associated with colon cancer were linked to rectal cancer. This finding suggests that the reason the combined analysis showed so many signals was that the colon cancer cases were driving the results, effectively drowning out the different biology of the rectum. The study confirms that colon and rectal cancers are not the same disease and that looking for a single set of markers for both is likely a mistake.

Among the many proteins identified, three stood out as the most reliable indicators for colon cancer risk. One of these, a protein called COMP, was found to be lower in people who later developed colon cancer. Another, known as MIC-1 or GDF15, was higher in those at risk, as was a third protein called TFF3. To ensure these findings were not just a fluke of the specific group of people they studied, the researchers checked their results against two other large groups of people in the United States and the United Kingdom. In these independent groups, the same three proteins showed similar patterns, reinforcing the idea that they are genuine markers of risk. The researchers also used genetic data to see if these proteins might actually cause the cancer or if they were just bystanders. While the genetic evidence was not definitive for all three, it provided additional support for the link between COMP and colon cancer, suggesting that the body's production of this protein might play a direct role in the disease process.

The study also looked at whether the signals differed between men and women or between different parts of the colon. They found that some proteins were more strongly linked to cancer in one sex than the other, and that the signals for the upper part of the colon were not exactly the same as those for the lower part. This adds another layer of complexity, suggesting that even within the colon, the disease may have different faces. The researchers noted that the blood samples were taken an average of ten years before the cancer was diagnosed, meaning these proteins are likely markers of risk rather than signs of an existing tumor. This is a crucial distinction, as it implies these proteins could one day help doctors decide who needs screening and how often, rather than just diagnosing someone who is already sick.

Despite these promising leads, the researchers are careful to state that these proteins are not yet ready for use in clinics. The study identified potential candidates, but more work is needed to prove they are useful for predicting cancer in the general population. The fact that the signals for rectal cancer were so weak in this study highlights the need for larger studies specifically focused on that area. For now, the most important takeaway is that the large intestine cannot be treated as a single entity. The body sends different messages depending on where a cancer begins, and future research must respect these differences to find the most effective ways to prevent and detect this disease. The discovery of these specific proteins offers a new path forward, moving away from broad, generalized approaches toward a more precise understanding of how cancer starts in different parts of the body.